Conversion of hydrocarbon oil



at {8, 1935'. R, F. mow 2,016,304

CONVERSION OF HYDROCARBON OIL Filed May 19, 1931 m n e FRESH RICH/78D ETBOW INVE TOR /-//6 ATTORNEY Patented Oct. 8, 1935 UNITED STTES PATENTOFFICE Richard F. Trow, Port Arthur, Tex., assignor to The TexasCompany, New York, N. Y., a corporation of Delaware Application May 19,1931, Serial No. 538,590

1 Claim.

This invention relates to the conversion of higher boiling hydrocarbonoils into lower ones and relates particularly to a method of distillinga clean cracking stock from a relatively dirty charge oil and crackingthe clean stock together with a refiux condensate which is formed in theprocess, a gas oil fraction stripped from a cracked residue which isformed in the process and a residue from the distillation step, in whichthe maximum practicable ultimate yield of a desirable light producthaving a high anti-knock value with a minimum yield of gas and carbon isobtained from the charge oil.

The invention broadly contemplates a method of cracking petroleum oilsto an ultimate yield of motor fuel and residue where a relatively dirtyhigher boiling oil such as unclean gas oil or topped crude charge oil isseparated by distilla-' tion and dephlegmation into a clean and a lessclean cracking stock and is subjected to appropriate cracking conditionsand a recycle oil resulting from the cracking operation is resubjectedto cracking while an ultimate tarry residue is discharged from thesystem.

The invention is especially adapted toa conversion process in whichsubstantially no liquid is carried in the reaction vessels of a coil anddrum type of apparatus. This process, now becoming popularly known aslow liquid level cracking, is one in which both liquid phase and vaporphase cracking is effected simultaneously in the same zone. It iscapable of being practiced at a higher temperature than is ordinarilyemployed in liquid phase cracking, and accordingly yields a producthaving a much higher antiknock value. It is also capable of beingpracticed at somewhat lower temperature than, true vapor phase cracking.

It has been found that the class of charge stock which is suitable forcracking in the liquid phase tends to precipitate and deposit coke inthe heater coil at the higher temperature em ployed in low liquid leveloperation. Therefore one of the main objects of the present invention isto develop within the system a stock cleaner than that charged to theordinary liquid phase cracking process from a relatively dirty chargestock. In other words the invention makes it possible tocharge anypetroleum oil containing an appreciable amount of crackable or gas oilconstituents to a cracking system and evolve therefrom a clean desirablecracking stock, and crack the stock under such conditions as to producea maximum yield of superior quality motor fuel and an ultimate residue.

It is not desirable to discharge an appreciable quantity of constituentsof the fresh charge oil from the system before it has been subjected toappropriate cracking conditions even though it is quite unclean. Thus afurther object of my 5 invention is to subject the residual fraction ofthe charge oil to suitable cracking conditions in the system so as to"effect such conversion into lighter products as is practicable.

In cracking oil in the conventional coil and drum type of apparatus thecontinuously developing residue, which is withdrawn from the drums,contains constituents which are capable of being further converted underfavorable conditions. T -ese constituents may be autogenously distilledfrom the residue by the sensible heat of the mixture under reducedpressure.

According to a preferred manner of regulating the conditions in thepractice of the process the fraction thus developed may besatisfactorily treated, or rather retreated, in the operation underconditions also favorable to the cracking of the clean somewhatrefractory cracking stock developed from the charge oil. Thus it isfound advantageous to auto-genously distill the residue developing inthe cracking drums to thereby strip out a gas oil fraction and recycleit to the cracking system for further treatment. In other words it isadvantageous to separate out and recycle gas oil portions of theproducts produced in the cracking step to thereby obtain an ultimateyield of only motor fuel and a heavy residue of pitchy consistency fromthe original charge oil.

These and other objects and advantages of my invention willbe betterunderstood by referring to the following description, taken inconnection with the accompanying drawing the single figure of whichillustrates in diagrammatical elevation a preferred form of apparatusfor practicing the invention.

Element l is a furnace, 2 is a reaction vessel, 3 is a combinationreaction vessel and scrubber, 4 is a dephlegmator, 5 is a refluxcondenser, 6 is a final condenser, 1 is a trap and 8 is an accumulatordrum. Element H] is a combination autogenous distillation anddephlegmating tower, II is a. condenser for the final vapors developedtherein, I2 is a trap and I3 is an accumulator.

A line l5 may conduct the fresh charge oil to preheater coils I6 and I1,situated in the reflux condenser 5 and dephlegmator 4, respectively, orby-pass either or both of them by manipulation of the valves 20, 2!, 22,and 23, and lead to the upper portion and/or lower portion of the vessel55 3. A vapor line 30 connects the upper portion of the vessel 3 withthe lower portion of the dephlegmator 4. A pump 32 takes suction thru aline 3| from the bottom of the dephlegmator 4' and discharges into acoil 35 situated in the furnace thru a line 33. A branch line34connected to the discharge side of the pump serves to furnish a refluxor scrubbing oil to the uppermost portion of the vessel 3.

The oil emerging from the coil 35 is passed thru another coil 36 in thefurnace I and emerges therefrom to be conducted to the upper portion ofthe reaction vessel 2 thru a line 40. A line 4| serves to connect thelower portions of the vessels 2 and 3.

A pump 43 takes suction on the bottom of the vessel 3 thru a line 42 anddischarges into the transfer line 40 thru a line 44 while a drain line45 leads from the bottom of the vessel 2 to the combination still anddephlegmator I0. A vapor line 50 connects the upper portion of thedephlegmator 4 with the reflux condenser 5 while a condensate run-backline 5| is also provided interconnecting the two vessels. A final vaporline 52 conveys vapor from the condenser 5 thru the final condenser 6 tothe trap l from which a portion of the liquid may be returned to theupper portion of the dephlegmator 4 thru the lines 53 and 54 by the pump55. The remainder of the ultimate distillate from the trap 1 is passedthru a line 56 to the accumulator 8, having a liquid outlet 51 and gasoutlet 58.

The residue delivered into the combination still and dephlegmator IDfrom the vessel 2 undergoes autogenous distillation at reduced pressurein the lower portion of the vessel It) and an evolved vapor is conductedto the upper portion thereof thru a line while a remaining residue isreleased thru a line ll. A pump 15 takes suction on the lower portion ofthe dephlegmating section of the vessel l0 thru a line 16 and dischargesthru a line H into the charge line 5 which leads into the vessel 3. Avapor line 8|) connects the upper portion of the dephlegmating sectionof ID with a condenser H. A portion of the condensate dropping out intothe trap l2 may be returned to the upper portion of the dephlegmatingsection of |0- thru lines EM and 82 and a line 821) having a valve 82aby a pump 83. The remainder of the condensate is conducted thru a line84 to the accumulator 3, having a liquid outlet 85 and a gas outlet 85.

When beginning to operate a sufiicient amount of clean oil may be drawnin thru a pipe 29 from a source not shown and pumped into the heater 35.After operating conditions are established a switch may be made to thefresh charge oil which is delivered thru the line I5.

In a preferred mode of operation a fresh charge oil which may be arelatively dirty gas oil or a topped crude, is charged thru thepreheaters l6 and I1 and emerging therefrom at a temperature ofapproximately 700 F. is split between the upper portion and the lowerportion of the vessel 3. That portion of the fresh charge oil deliveredto the bottom of the vessel is introduced below the surface of the smallbody of liquid carried therein which is ordinarily only enough to insurea liquid seal so that no vapors are withdrawn from this vessel. 3 a

That portion of the charge which is discharged to the upper portion ofthe vessel 3 is delivered at about a midpoint of a series of baffleplates which serves to distribute the liquid in a filmlike manner toeifect contact with the hot vapors moving upward towards the outlet pipe30. Va.- pors leaving the vessel 3 at a temperature of about 810 F. areconducted thru the line 30 into the dephlegmator 4 where dephlegmationis effected to produce overhead vapor and a reflux 5 condensate. Thereflux condensate is cooled somewhat in the lower portion of thedephlegmator 4 by the indirect contact of the charge oil which is passedthru the preheater section I! and is withdrawn therefrom at atemperature of 10 7 about 750 F. and. pumped thruthe heater.coils by thepump 43 and are discharged into the transfer line 40 near the outletfrom the heater coil.

The thus combined highly heated clean cracking stock and residue fromthe vessel 3 having an 20 average of about 880 F. is delivered into theup- 7 per portion of the vessel 2. A large portion of the productsremaining liquid at the entry to vessel 2 are immediately flashed intovapor. Some atomization of the liquid occurs also due 25 to thevaporization and rapid separation of portions of the oil from the mainstream being delivered into the vessel 2 under a preferred pressure ofabout 400 pounds per square inch which pressure is preferably maintainedthroughout 30 the remainder of the cracking portion of the system. I

' The vapors and some entrained .or suspended finely divided liquidparticles are passed thru the vessel 2 and into 3 by the connecting line4| 85 While liquid portions being deposited in the bottom of the vessel2 are preferably drawn off as soon as they are deposited. In some casesit may be desirable to maintain such an amount of liquid in the vessel 2as to overflow small quantities 40 of it thru the line 4| into thevessel 3.

The hot vapors entering the vessel 3 move upwardly encountering thatportion of the combined fresh charge and recycle oil which is droppingdown from the bafiies' above. Cooling and con- 5 densation of the vaporsis thus effected to a desired extent and the hot vapors in turn serve to'impart enough heat to the combined fresh charge and recycle oil tovaporize a portion of it. After encountering the charge oil, the up 50wardly moving vapors encounter the clean scrubbing oil which isdelivered to the uppermost portion of the bafiies thru the line 34, aspreviously described, and are still further cooled and cleansed andfinally emerge substantially free of 55 carbonaceous or dirty materialthru the line 30. In order to reduce the amount of scrubbing oilrefluxed to the top of 5 thru the line 34 it may be found desirable tocool it after it leaves the pump 32 and before it is discharged into thevessel. 0 That portion of the oil which fails to vaporize and thatwhichremains condensed in the vessel 3 is deposited in the bottom thereof incontact with that portion of the combined fresh oil and recycle oilbeing delivered thereto which serves 5 to further cool the liquidportion being deposited. The amount of cooling supplied here should beat least sufiicient to lower the temperature of the combined oils belowWhere advanced cracking or cracking to pitch or coke of the leastrefractory 70 constituents occur. It is in fact preferable to maintainonly a temperature at which cracking of the heavier less refractoryconstituents begins and substantially all of the lighter more refractoryconstituents of the charge oil and the refluxed oil will have becomevaporous at the pressure employed. The resultant vapors from the chargeand reflux material are added to those moving upwardly to the top of thevessel while the remaining liquid is withdrawn thru the line 42, aspreviously described.

The warm vapors conveyed thru the line 30 to the dephlegmator 4 aresubjected to any conventional method of fractionation in the firststages of which heat is interchanged between them and the fresh chargewhich is being passed thru the preheater coil H. The dephlegmated vaporsare passed thru the reflux condenser 5, where heavier portions arecondensed, and a portion of their heat is imparted to the fresh chargewhich is being passed thru the coil 56. The final vapor is conductedthru the line 52 to the final condenser E and to storage while a portioncondensed in the condenser 5 is returned to the upper portion of thedephlegmator t thru the line 5|, as is also a portioncondensed in thecondenser 6 and trapped out in the trap I, as a reflux cooling medium.

The residue resulting from the reaction and being deposited in thevessel 2 is released thru the line 45 into the lower portion or stillsection of the vessel H] where autogenous distillation is effected at areduced pressure. The resulting vapors are conducted to the upper ordephlegmating section of the vessel thru the line it while the heavyresidual portion is released from the system thru the line H.

The vaporous portion conducted to the dephlegmating section of thevessel is subjected to any conventional method of fractionation thereinto produce a relatively small percent of final overhead vapor and areflux condensate. The vaporous product is comparable to that emergingfrom the previously described reflux condenser 5 and is condensed in thecondenser it and passed thru the accumulator to storage or a portion ofit may be returned to the upper portion of the dephlegmating section asa reflux cooling medium. The reflux condensate collects in the bottom ofthe dephlegmating section of i9 and, as it is capable of being furtherconverted under the cracking conditions established in the crackingzone, is withdrawn by the pump it and delivered into the line i5 tothere combine with the fresh charge and be delivered into the vessel 3as previously described.

In the mode of operation which is described herein the approximatetemperatures given are well above the economical and practical operatinglimits of a liquid phase cracking operation, that is, one where sizablebodies of liquid are maintained in reaction vessels such as 2 and 3. Bymaintaining temperatures of these higher orders it is possible toproduce an ultimate distillate which has a relatively high anti-knockvalue and because of the shorter times of reaction in the reactionvessels of a combined vapor and finely divided suspended liquidparticles, as compared with only a body of liquid, no secondary oradvanced cracking in which pitchy or cokey bodies and noncondensablegases are ordinarily formed, has time to occur. On the other hand as therate of cracking is greater at these higher temperatures a yield oflighter products based on the fresh charge will be obtained which is asgood economically speaking as that obtained from average liquid phaseconversion.

It is pointed out, however, that in order to maintain these desirablehigh temperatures it is necessary to provide a cracking stock, that is,the

oil passed thru the heater coils 35 and 36 which is much cleaner thanthe usual charge oil for a coil heater in a coil and drum type apparatuswhere cracking in the liquid phase. This is because relatively uncleancracking stock contains constituents which are not capable of beingsubjected to the higher order of temperature maintained in my coilwithout readily precipitating cokey particles which deposit in the coilsand greatly shorten the time of a single continuous 10 operation.

The formation of these bodies is believed to be due largely to moreadvanced cracking of the less refractory heavier constituents of thedirtier oils and it may be also due to some substances which may bepresent in the oil tending to promote the formation of coke due to theaccelerated rate of reaction that occurs in the coil at the highertemperature.

In my invention the higher temperature to which the clean cracking stockis heated in the co l immediately quenched or lowered upon its oxiu remthe coil by the addition of a somewhat cooler oil. This quenching mediumconsists of the previously referred to less refractory or dirtyconstituents of the fresh charge oil, the heavier portion of recycle oilfrom the residue stripper residue precipitating from the cracked.products entering thru the pipe ii i. This temperature is only lowered,however, to one at which a desirable further reaction of all of the oilbeing treated will continue but at a somewhat slower rate. The combinedoil thus undergoing treatment is delivered into the reaction vessels forfurther time of digest as has been described.

The quenching oil, added to the hotter material which is beingdecomposed at a faster rate, serves not only to lower the temperatureand thus slow up the rate of decomposition but also acts as a solvent,it is believed, for incipient pitchy or cokey particles and gas whichmay be present in the highly heated oil from the coil and which woulddoubtless evidence itself positively in the reaction vessels if thisquenching and solvent oil were not added at this stage before secondaryreaction begins.

It is pointed out that among the conditions established in thisoperation is that of subjecting the vapors to a longer time of digest inthe vessels than the liquid is subjected to. The time of digest of thevapors runs from their entrance thru pipe 40 to their emergence thrupipe 30 while the liquid is withdrawn from the bottom of each vessel assoon as it is deposited.

As an alternative mode of operation to the one previously describedherein, the charge oil may be delivered directly into the upper portionof the vessel through; pipe 98 having a valve 9|, cutting out coil l1and perhaps l6 and delivering all of the liquid from the upper sectionof ID, as before, thru the line i! into the vessel 3, while all of thecondensate from the condenser ll may be refluxed through a line S2having a valve 93 as a coolant to some point in the dephlegrnator 4 toreplace the cooling furnished, as shown and described, with the chargeoil passing thru coil 11.

A suitable clean cracking stock for passing heating coil 35 may be a gasoil having a straw or light straw color or an oil of 15-20 on the cell,Lovibond scale; however, the use in this stage of other relatively cleancracking stocks is not precluded.

While a preferred mode of operation has been described herein in detailit is to be understood that neither this form nor the approximatetempassing a condensate oil produced in the process through a heatingcoil in which the oil is subjected to a high cracking temperature,delivering the heated products of cracking into an enlarged crackingzone maintained at cracking temperature under superatmospheric pressurewherein separation of vapors from liquid takes place, directing theseparated vapors to a combined cracking and dephlegmating zone, passingvapors at a temperature within the cracking range from said combinedcracking and dephlegmating zone to a high pressure fractionating zonewherein fractionation occurs to separate out a condensate, passing saidcondensate to aforesaid heating coil forcracking, withdrawing liquidfrom said enlarged cracking zone at a rate adequate to prevent theaccumulation of liquid therein, expanding the liquid thus withdrawn intoa low pressure auto-distillation zone wherein separation of vapors fromliquid takes place, passing the separated vapors into a low pressurefractionating zone and subjecting them to fractionation therein,bringing charging stock intoindirect heat 5 exchange with vapors in saidhigh pressure fractionating zone, introducing charging stock thus heatedinto said low pressure fractionating zone to dephlegmate the vaporstherein, withdrawing Y a liquid fraction from said low pressurefraction- 10 ating zone comprising reflux condensate and unvaporizedconstituents of the charging stock and introducing the admixed oils intosaid combined cracking and fractionating zone wherein the oil issubjected to fractionation and cracking, with- 15 drawing a residualfraction from said combined cracking and fractionating zone and passingit to said enlarged cracking zone wherein the time of subjectionofliquid components to cracking 1 conditions is limited by the rapidwithdrawal of 0- liquid from the chamber while vaporous constituents aremaintained at cracking temperature therein. l

RICHARD F. TROW.

